2 Answers
2

Short answer: The rules do not cover this one way or the other, although they strongly imply that they should. The published errata do not address the situation either, leaving it up to GM fiat.

Long answer: I went through the (English translation of the) rules, and it sure seems like there should be a way to reduce Stress other than via Stress Explosions, mainly because Butlers explicitly do not have Stress reductions over time (see p. 49). That certainly implies that Maids should.

Except, well, they don't. There are a couple of abilities (like Cooking) that can reduce Stress, plus the explicit use of Favor, but if there's a rule regarding the actual reduction of Maid Stress in downtime it's nowhere in the English translation.

Perhaps it's meant to refer to some ability of Maids to reduce their Master's Stress over time. Except, well, rules covering that don't seem to be in the book either. Awesome.

The official errata do nothing to address this one way or the other, leaving the situation up to GM fiat. Since the rules imply that Maids reduce Stress over time, a house rule handling it should probably take time into account.

Edit: Further reflection shows that, of course, what would
really be proper for Maid is yet another random table
to handle stress reduction. Such a table is left as an
exercise for the reader.

No. Rules as written, Stress never resets automatically to zero except after a Stress Explosion. However, the game's translator posted on Twitter that he believes it would be a reasonable house rule:

Ewen Cluney

The game is vague about between-session stuff, but I would reset Stress to 0 unless it's a very direct continuation.

By a technicality, however, any maid can reset their Stress to zero between sessions, by intentionally triggering a Stress Explosion immediately before the end of the game session. Since the duration of the Stress Explosion is measured in minutes of real time, "including when you take a break from the game" (page 23), you will begin the next session with zero Stress and the Stress Explosion already over.

Aside from this, there are a number of ways to remove Stress. The full list of ways to reduce Stress all the way to to zero is as follows:

A Stress Explosion reduces the character's Stress with the passage of time, at a rate of 1 point per minute of real time, until it reaches zero (page 23)

If the optional Comforting rule is in use, a character can accept a Stress Explosion early and reduce their Stress to zero. For each character who works together, the maid removes an additional point of Stress per minute. If the characters role-play it, the character can remove an additional 1d6 to 3d6 Stress at the GM's discretion. (page 73)

A maid wearing Bikini Armor who undergoes a Stress Explosion may lose the armour to drop Stress immediately to 0 (page 82)

The item Phoenix Maid Uniform allows the user to reduce their Stress to zero once per session (page 98)

The item Pipe Organ of Memories removes 2d6 Stress from anyone who can hear it (page 109)

The item Secret Garden allows you to remove an additional 1d6 to 2d6 Stress (page 110)

A Romance Event allows two maids to comfort each other to remove all Stress (page 112)

An Action Event allows everyone to remove 2d6 Stress (page 113)

In the scenario "Maidenrangers of Love and Justice", one of the Items of the Master's Memories allows you to remove an amount of Stress (page 173)

In the scenario "Maidenrangers of Love and Justice", card 3 allows you to remove 2d6 Stress (page 174)

However, the following situations prevent the removal of Stress "with the passage of time", the only method for this in the rules being the Stress Explosion:

A butler does not have a Stress Explosion (page 49)

Maids cannot remove Stress with the passage of time while the Master is having a Stress Explosion (page 59)

A maid cannot use her Stress Explosion or use Maid Powers when wearing an alternate costume (page 79)

Any character who has caused a maid wearing a Funeral Kimono to gain stress in the current session cannot remove Stress with the passage of time (page 88)

In the scenario "Miko RPG!", the characters are shrine maidens and cannot remove stress with the passage of time (page 158)

Although there are numerous references to "removing stress with the passage of time", the only mechanic which removes stress over time is the Stress Explosion. In the initial printing of the book, the rules for butlers (page 49) said that "Butlers cannot remove Stress with the passage of time", implying that Maids can. However, the second printing of the book revised this to clarify that:

Lacking Stress Explosions, Butlers cannot remove Stress with the passage of time and must spend Favor to remove it instead.

This clarifies that the only way for a character in Maid RPG to remove stress with the passage of time, rules-as-written, is the Stress Explosion.